Semiconductors have been used in optical transmission devices. For example, silicon has been used in integrated silicon chip devices. Such devices may include silicon waveguides formed as an integrated circuit on a silicon dioxide layer supported by a silicon substrate. It is known that silicon exhibits a refractive index varying with temperature. It exhibits a refractive thermal non-linearity dn/dT=1.86.times.10.sup.-4 K.sup.-1 at a wavelength of 1550 nm. This non-linearity with application of heat has been used to form phase modulators in silicon and silica based waveguide devices by using a thin metal track over the waveguide region to provide a resistive heater.
It is an object of the present invention to provide an improved structure and method for effecting resistive heating in a thermo-optic semiconductor device.